In the simplest terms, the spine is a column made of vertebrae and discs. The vertebrae provide the support and structure of the spine while the spinal discs, located between the vertebrae, act like cushions or “shock absorbers.” These discs also contribute to the flexibility and motion of the spinal column. Over time, the discs may become diseased, infected, develop deformities such as tears/cracks, or simply lose structural integrity, for example, bulge or flatten. These impaired discs can affect the anatomical functions of the vertebrae, due to the resultant lack of proper biomechanical support, and are often associated with chronic back pain. Chronic back pain afflicts a large percentage of the world's population and often interferes with one's ability to participate in regular daily activities.
Several surgical techniques have been developed to address spinal defects, such as disc degeneration and/or deformity. Spinal fusion has become a recognized surgical procedure for restoring biomechanical and anatomical integrity to the spine. Spinal fusion techniques involve the removal, or partial removal, of at least one inter-vertebral disc and preparation of the disc space for receiving an implant by shaping the exposed vertebral endplates. An implant is then inserted between the opposing endplates. Vertebral endplates can have complex shapes due to various anatomical and biological factors. For example, a vertebral endplate may be concave in some portions. The vertebral endplates may also have surface irregularities and even bony protuberances, or osteophytes, which can be difficult to remove. These osteophytes, found predominately about the posterior-lateral portions of the endplate, are especially problematic as they can painfully impinge on nearby anatomical structures and reduce the useable implant-seating surface to primarily the medial-anterior portion of the disc space. This reduction in seating area may compromise biomechanical integrity by reducing the area in which to distribute mechanical forces, thus increasing the apparent stress experienced by both the implant and vertebral endplate.
Proper endplate preparation is important to successful spinal fusion surgery procedures. To achieve fusion, it is generally necessary to expose bleeding endplate bone stock. This initiates the biological healing process of the bone and encourages implant integration. The surgeon must also conform or shape the endplate to, at least, approximate the implant geometry thereby ensuring proper seating of the spinal implant in the disc space. One of the many challenges of preparing the endplates is the discrepancy between the shape of the endplates and the implant. While the spinal endplates may have a complex surface topography, the mating surfaces of spinal implants are generally flat. Thus, the surgeon may initially desire to provide the maximum surface area for proper implant seating by simply razing enough endplate bone stock to ensure a relatively flat surface.
In addition to maximizing the surface area available for implant seating, the surgeon should also preserve as much surface vertebral endplate bone as possible by minimizing the amount of bone removed since this subchondral bone is generally much stronger than the underlying cancellous bone. Preservation of the endplate bone stock ensures biomechanical integrity of the endplates and minimizes the risk of implant subsidence. Thus, the surgeon should provide for optimal seating of the implant while still maximizing the amount of available securing endplate bone stock.
The surgeon may rely on a number of instruments during complex spinal surgical procedures. With the advent of spinal fusion surgery and the development of spinal implants, there is an increasing need for complimentary instruments. These complimentary instruments should reduce the “instrument load” on the surgeon while increasing the efficiency and precision of the surgical procedure. These instruments should also compliment the final size and shape of the implant to be used, again increasing the efficiency of the surgical procedure, while decreasing the overall need for multiple instruments. While there are many instruments that may be required for such complex spinal surgical procedures, there is a need in the art for a single instrument suitable for preparing vertebral endplates to properly receive a spinal implant for spinal surgery procedures.
Methods of endplate preparation have traditionally been performed “by-hand” using a variety of instruments. Traditional free-hand instruments such as box chisels, osteotomes, curettes, drills, milling instruments and the like, which aid in shaping the endplate, also aggressively, and sometimes unevenly, remove bone. Even when used by the most skilled surgeons, these traditional free-hand instruments may prove difficult to control in order to achieve uniform and reproducible results during endplate preparation. The surgeon must also avoid damaging nearby anatomical structures, such as the spinal cord or vertebral arteries. These previously known “by-hand” methods and instruments are generally cumbersome, lack precision, and may lead to the removal of excessive amounts of vertebral endplate bone stock.
None of these approaches provide a single multi-purpose surgical instrument, as is now taught, for allowing controlled and precise preparation of vertebral endplates while preserving endplate bone stock. Thus, there is a need in the art for a single spinal surgical instrument which reduces the instrument load and the number of operating steps for a surgeon, improves visualization of the disc space while minimizing exposure of the disc space, and improves surgical safety by increasing the precision of complimentary free-hand instruments while reducing the risk of damage to nearby anatomical structures.
There is a further need in the art for an instrument for the improved preparation of spinal endplates, especially one which can be used to prepare the posterior-lateral regions of the endplates and/or the entire endplate. There is also a need for a single instrument that can be flipped about its longitudinal axis outside of the disc space, and re-inserted to address features of both the left and right posterior-lateral regions of a vertebral endplate. For example, a single multi-purpose instrument should be capable of preparing both the lateral and contra-lateral sides of a vertebral endplate. Still further there is a need for a single instrument capable of preparing both the left and right posterior-lateral regions of vertebral endplates and for removing osteophytes.